The human cornea provides about two-thirds of the refraction of the eye. Thus, its shape is of great interest to optometrists and ophthalmologists who must provide a patient with sharp vision. Although there are various methods to measure the corneas, the most popular commercial systems are based of the principle of measuring a pattern reflected off the cornea. The pattern most often used for this purpose is a set of concentric rings. One problem with concentric ring patterns is that it is difficult to know the exact point of correspondence between a point on the reflected pattern source and its image reflected off the cornea. If the cornea is not axially symmetric, the surface normal of a point on the cornea will not lie in the meridional plane of the measurement system and thus, the point of light originating on the reflected pattern source will not lie in the same meridional plane. To directly measure the point of correspondence, polar and rectangular checkerboard patterns have also been proposed, but have not become popular in commercial systems.
One problem with this polychromatic target approach is that color cameras or multiple band pass cameras must be used in the system. This increases the parts and manufacturing cost associated with the instrument. To overcome this limitation, we present a monochromatic multi-resolution target that provides most of the benefits of the polychromatic multi-resolution target, but reduces the parts and manufacturing costs so that the instrument is more competitive in the commercial marketplace.
A corneal topography system measures the power and shape of the cornea so that a clinician can use this information to evaluate or treat a patient's vision. One of the most popular methods for measuring this corneal information involves reflecting a light target off the cornea. By analyzing an image of the reflected target, the power and shape of the cornea can be determined. In our previous patent U.S. Pat. No. 6,926,408 we described why a polychromatic multi-resolution corneal topography target can help improve on corneal measurements.
The instant invention relates to a corneal topography system that measures the power and shape of the cornea so that a clinician can use this information to evaluate or treat a patient's vision. One of the most popular methods for measuring this corneal information involves reflecting a light target off the cornea. By analyzing an image of the reflected target, the power and shape of the cornea can be determined. In applicants' U.S. Pat. No. 6,926,408, it was described why a polychromatic multi-resolution corneal topography target can help improve on corneal measurements.
The instant invention provides a method to encode both high-resolution and low-resolution reflected images of a cornea to improve the measurements for reflection based corneal topography systems.